Construction of iron-truss bridges



UNT

mon.

SQUIRE WHIPPLE, OF UTICA, NEW YORK.

CONSTRUCTION 0F IRON-TRUSS BRIDGES.

To all Lo/wm may concern:

Be it known that I, SQUIRE i-IIPPLE, of the city of Utica, county ofOneida, and State of New York, have invented a new and usefulImprovement in the Construction ot' a Bridge by me called an Tron-TrussBridge,7 which contains principles also advantageously applicable in theconstruction of wooden truss bridges, and that the following is a fulland exact description thereof, reference being had to the accom-Vpanying drawings.

This bridge consists of a licor ot plank and timber similar to anordinary bridge lioor, sustained by two or more trusses of iron. Seedrawings Figure l. Each truss consists of an arch a, a, of castironextending the whole length of the span, one or more thrust ties T, T,extending along through or near to the chord of the arch,

and connected with the lextremities thereof,V

ing horizontally from the end oit' the arch to v the foot of the firstvertical rod from the end, Fig. 5; horizontal plates, nearly square inform, and placed diagonally forming a support for the floor beams andthrust ties, and affording points of attachment for the vertical anddiagonal pieces. These are the essential parts of the truss, and Iproceed to a more particular description of each and the manner offorming and connecting them.

The arch is formed in sections or segments, Fig. 3, of from ten totwelve feet or any suitable length. The middle segment letter a, Figs.3, and 4, may be in the form of an inverted trough, with its width forarches from to 8O feet about the top part of the span of the arch, thedepth about half of the width and the thickness of metal about one-tenthof the width, size, form and proportions to be varied according tocircumstances or the taste and views of the engineer. The segment letterb, Figs. 3, and 4, next the middle is to be made of the same form andsize, but separated vertically and longitudinally in the center, theparts thus formed, remaining together at the end to ward the middle, butdiverging slightly toward the other end, where they are connected `by across bar e, Fig. 3, forming the whole into a solid piece with a slit oropening in the middle extending to within ten or twelve inches of thewider end, and running to a point toward the other. The next segment,letter c, Figs. 3, and 4, is formed and separated in the same way, onlyhaving the openings in the middle wider and more divergent toward theend of the' arch, the narrower end being of the same width and matchingwith the wider end of the preceding. The remaining segments to be formedand adapted to the preceding in the same manner last described, but`increasing in width and divergence to the end of the arch, where thewidth may be about three times as great as at the middle, with the samearea in the cross section except at the cross bars connecting the twohalves or" the segments, Fig. 4. These cross bars should have greaterthickness than the other parts of the segments and be cast with holessix or eight inches tro-m the ends of the segments for the vertical rodsto pass through or in case a single vertical rod is used at each joint,the hole should be formed immediately at the joint by a semicircularnotch in each of the two contiguous ends.

At the joints of the arch the segments a, Fig. Q, should be furnishedwith projections or extensions from their ends lapping past the jointand interlocking in such a manner as to keep the ends in place, and ifnecessary,

vsmall bolts may be passed through these lap-- ping portions tostrengthen the joints. To give the diagonal ties a more uniformobliquity, the segments may be made shorter toward the ends of the arch.

It will readily be seen from the manner of forming and connecting thesegments, that the top of the arch, Fig. 3, will present the appearanceof two horizontal arches touching one-another in the middle and curvingequally therefrom in opposite directions to the ends. This form beinggiven it to produce stiffness and sustain it against lateral Hexure.

The thrust ties are two to each truss, one under each side of the arch,though any dilterent number of arrangement may be adopted. They may becomposed of fiat bars of a manageable length placed horizontally andconnected together by locking and banding, in the manner of which Fig. 7of the drawings presents an edge view or any other suitable manner. Theconnection with the toes or extremities of the arch may be in the mannerrepresented in Fig. G. Or the ties may be in the form 'of chainsconsisting of a number of long links formed ol" round bars and connectedby clevises and pins, the end links embracing the toes or extremities ofthe arch and being kept in place by a notch or shoulder at or near theend of the arch.

The size of the thrust tie will depend upon thelength o" the arch. Theweight it is to be subjected to and the rise of the arch abovethethrusttie. 1

When the rise of the arch above the thrust tie is `from one tenth to oneeighth of the length of the span, thrust ties having an aggregate crosssection of about one square inch for each hundred square feet of bridgefloor will be about a suitable size in ordinary cases.

The vertical rods may be made oi round ir'on, and in all casesshouldhavean aggregate strengthsuiiicient to sustain the floor and any additionalweight that may come thereon, and when the wrought iron dia-g-,

onal tie is used, the vertical rods should have a larger `size togivethem stiffness as post-s. They are two at each joint (though oneonly may be used) at from 12 to 16 inches dista-nce from one another toadmit the floor beams between. These rods have a screw and two nuts ateachend, Fig. 8. Previous to putting them into the structure, one nut isscrewed onto each end a and b, Fig. 8, to a distance ofsix or eightinches from' the end toward the middle of the rod. The upper end is thenpassed through a loop oreye formed on the upper endof the diagonal tie,Fig. 8, then through the hole in the arch segment and secured by a screwnut on the top. The lower end is passed through a loop on the lower endof that diagonal tie which is opposite to the one attached as aforesaidto upper end of the same vertical rod. Then passing down through thelower or square plate, is secured by a nut below. The uppermost of thetwo lower nuts a, Fig. 8, serves to` regulate the tension of thediagonal tie and prevent its sliding up, while the lowermost nut b, Fig.8, at the upper end answers a similar purpose, preventing the verticalrod from being thrust up through the loop of the diagonal tie and thehole in the segment of the arch.

When the cast iron brace is used instead of the wrought iron diagonaltie, the vertical rodis never subjected to a thrust or negative forceand may be of smaller size and furnished Vonly with a bolt head at oneend and a screw-nut at the other, like van ordinary bolt. Otherwise,there may be one or more posts of cast or wrought iron used inconjunction with the wrought iron diagonal ties, in which case thevertical rods may be made smaller, or dispensed with entirely, thediagonal ties being enlarged so to be adequate to sustain the wholeweight.

The mode of connecting the diagonal ties with the other parts has beenexplained in speaking of the vertical rods, and it is only necessary toadd that they may be of round iron from one to one and a half inches indiameter according to circumstances. It may also be proper to add thatin case a single vertical rod be used at each joint of the arch, twodiagonal ties are connect-ed with each end thereof by loops in theinanner above described, viz, one descending obliquely to the right andleft from the upper end, and ascending obliquely to the right and leftfrom the lower end of the vertical rod.

The square horizontal plates, Fig. 5, may be of wrought iron fromfourteen to sixteen inches square and from to 1 inch thick placeddiagonally under the floor beams with two opposite angles projecting onopposite sides of the beam, and' pierced for the vertical rods to passthrough. The remaining angles, Fig.\5, projecting under the thrust ties,and being turned up at the points to support the sag of the ties andprevent them from spreading. These last mentioned angles may beelongated if necessary toward the ends of the arch, where the tie barsare farther asunder.

`The thrust ties may be dispensed with and the thrust of the arch besupported by the abutments and piers upon which the bridge rests. Theother parts of the truss being the same, or nearly so, as when thethrust ties are used. In such cases the abutments may be strengthened bya slope wall or frame work of timber s, Fig. 1, on the back side,ext-ending into the earth so as to form nearly a continuation of thearch of the truss, and if necessary piles fr', r, Fig. l, may be drivenobliquely into the earth in continuation of the curve, or sheet pilingm, Fig. 1, driven toward the center of the arch, to support the foot ofsaid slope wall or frame work.

In bridges of a long span where the arch rises high above the floor ofthe bridge, the diagonal ties may not extend quite down to the floor butterminate at their lower extremities in another arch between the Hoorand the principal, or cast iron arch, being here connected and steadiedby light ties of wrought iron, forming the` intermediate arch asaforesaid.

The application of the expansion or divergence of the `parts of thearch, or main braces of wooden truss bridges may be effected in thefollowing manner. If the span be so short that the timbers to sustainthe thrust of the arch may be conveniently obtained of the whole length,these timbers A, Fig. 10, may be split with a pitsaw for about one thirdof their length from each end, and the ends sprung and braced apart,more or less, according to the length and the proposed degree ofdivergence to be given to the braces. Then the braces (or arch segments)running up from the ends of the truss, must be two at each end,corresponding in thickness horizontally with the halves of the splittimbers below, to which said braces are adapted and secured at the endof the truss. Or the lower timbers may be split for their whole length,and the two halves Xed apart to adistance equal to the proposeddivergence of the braces above.

In case the span be greater than is convenient (B, Fig. 10,) to procurethe string timbers or thrust ties, these may be formed of a timber a, B,Fig. 10, in the middle of about two thirds the length of the truss, uponwhich may be lapped or spliced other timbers, b, b, b, ZJ, B, Fig. 10,one on each side (horizontally) of both ends of the same vertical butless horizontal thickness, eX- tending to the ends of the truss. Theselater timbers being so chamfered as slanted upon the part lapping ontothe other timber, as to give them the required divergence at theiropposite ends. These lap joints' may be secured by iron bolts passingthrough horizontally with iron straps if necessary7 and furtherstrengthened by pieces of wood or metal (c, c, and c., B, Fig. 10,)driven or fitted vertically into corresponding notches or mortises inthel contiguous or splicing may be used with safety of a greater spanthan when no such precaution is taken to prevent lateral iieXure. Or awooden arch may be formed in sections or segments, diverging toward theends (of the arch) in a manner similar to that of the cast iron archabove described secured by braces and thrust formed by the continuedsplicing of timbers, or having the thrust sustained' b abutments andpiers.

Now what I claim as my invention in t-he above described improvement,and desire to secure by Letters Patent, is-

l. The method of sustaining the flooring of bridges by iron trussescontaining castiron arches formed in sections or segments, incombination with diagonal ties or braces, to sustain the form of thearch against the eifects of unequal pressure, (with or without verticalposts or rods,) and wrought iron arch strings or thrust ties to sustainthe thrust and prevent the spreading of the arch, in case t-he abutmentsand piers be not relied on for the purpose.

2. Also, the divergence or horizontal eX- pansion of the arch from themiddle portion to the ends thereof, in wooden trusses or arches as wellas in those composed of iron.

SQUIRE WHIPPLE.

Witnesses: a

JOHN PARSONS, GEO. J. HOPPER,

